In a switching power source device configuring an AC/DC converter for converting an AC voltage to a DC voltage, a PFC circuit is widely used to reduce the power factor degradation and occurrence of harmonic noise due to the phase difference between the input voltage supplied from an AC power source and the input current.
In the past, various switching power source devices including PFC circuits have been realized mainly by an analog control. For example, in Patent Documents 1 and 2, there are disclosures as the prior art switching power source device including an analog control PFC circuit.
However, in order to meet the recent demand for cost reduction, easy tuning, and the like, the control method of various switching power source circuits including PFC circuits has been replaced by that mainly base on digital control. More specifically, a control part for controlling the ON/OFF of a switching element (MOSFET, and the like) to control the current flowing through a coil in a PFC circuit has been replaced by a program process device such as a microcontroller (hereinafter, simply referred to as micon) from a conventional analog IC (Integrated Circuit) including an error amplifier. For example, in Patent Document 3, there is a disclosure as the prior art AC/DC converter including a PFC circuit of digital control method.